Immunohistochemical detection of PD-L1 in small cell lung cancer and its prognostic values

The molecule known as Programmed death-ligand 1 (PD-L1) exerts an inhibitory effect on immune system reactions and promotes cancer progression. Its prognostic role in small cell lung cancer (SCLC) remains less defined than in non-small cell lung cancer. This study aimed to evaluate PD-L1 expression and its prognostic value in SCLC, comparing detection by immunohistochemistry (IHC) and reverse transcription quantitative polymerase chain reaction (RT-qPCR).

PD-L1 expression was assessed in paired tumor and non-tumor tissues from 66 SCLC patients using IHC and RT-qPCR. IHC positivity was defined as membrane staining in >5% of tumor cells. Associations with clinicopathological factors were examined by Fisher's exact test. Survival analysis employed Kaplan-Meier curves and log-rank tests. Univariate and multivariate Cox regression identified independent prognostic factors.

IHC analysis showed PD-L1 positivity in 34/66 patients. RT-qPCR revealed significantly higher PD-L1 mRNA levels in tumor versus non-tumor tissues (P<0.01). Both IHC positivity and high mRNA levels were associated with larger tumor size, metastasis, and advanced clinical stage (all P<0.05), but not with age, gender, or smoking/drinking history. Patients with PD-L1-positive IHC staining or high PD-L1 mRNA exhibited significantly worse 5-year overall survival (P<0.05), with IHC showing stronger prognostic discrimination. Multivariate analysis confirmed IHC positivity (HR=2.45, P=0.004) and high mRNA level (HR=2.12, P=0.012) as independent predictors of poor survival.

PD-L1 expression is associated with aggressive clinicopathological features and independently predicts poor survival in SCLC. IHC appears to be a more sensitive detection method than RT-qPCR for prognostic assessment.